<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<style>
#one{width:100px;height:100px;background:red;position:absolute;}
</style>
<script>
window.onload=function(){
	var one=document.getElementById("one");
	var disx=0;
	var disy=0;
	one.onmousedown=function(e){
		var ev=e||event;
		disx=ev.clientX-one.offsetLeft;
		disy=ev.clientY-one.offsetTop;
		
		document.onmousemove=function(e){
		var ev=e||event;
		var l=ev.clientX-disx;
		var t=ev.clientY-disy;
		if(l<0){
			l=0	
		}else if(l>document.documentElement.clientWidth-one.offsetWidth){
			l=document.documentElement.clientWidth-one.offsetWidth;	
		};
		
		if(t<0){
			t=0	
		}else if(t>document.documentElement.clientHeight-one.offsetHeight){
			t=document.documentElement.clientHeight-one.offsetHeight
		};
		
		
		one.style.left=l+'px';
		one.style.top=t+'px';
		};	
		
		document.onmouseup=function(){
			document.onmousemove=null;
			document.onmouseup=null;	
		};
		return false;
	};
};

</script>
</head>

<body style="height:2000px;">
<div id="one">

</div>
</body>
</html>
